RNAi-mediated control of spotted wing drosophila (Drosophila suzukii): efficacy challenges and biosafety considerations

Abstract: Drosophila suzukii Matsumura (Diptera: Drosophilidae) is a rapidly emerging invasive pest in America and Europe. First described in Germany in 2011, high yield losses were already recorded in 2014 in cherries, small fruits and grapevine. Pesticide and mechanical control measures have been applied which are neither environmentally nor economically sustainable. As D. suzukii is well established in Germany, long-term solutions have to be developed. In this regard, RNAi-based pest control strategies could have potential. However, a major bottleneck is delivery of RNA molecules and efficacy of control. D. suzukii attacks intact maturing and ripening fruits and damage is produced by the developing larvae inside the fruits. D. suzukii can rapidly produce high population densities. Fruit damages caused by D. suzukii can serve as entrance for additional pests and microbes, which is of major concern in grapevine. Therefore, RNAi-mediated control has to aim at adult flies before egg deposition in fruits and has to be efficient against high population densities. Furthermore, RNAi-mediated shut down of D. suzukii genes has to occur rapidly. Challenges are therefore finding the right target gene and developing an efficient delivery method. As RNAi in D. suzukii is not systemic, a constant dsRNA uptake either through transgenic plants or through oral feeding seems necessary. We tried to induce gene knock down through oral application of dsRNAs for essential genes like tubulin (γTub23C) or vacuolar ATPase (Vha26), however, with limited success. Another challenge is biosafety considerations and avoidance of off-target effects in non-target insect species.